Among systems in which power is wirelessly transmitted from a power transmission device to a power reception device, there is a system that uses an electric field coupling scheme. In this system, electrodes of the power transmission device and electrodes of the power reception device are electric field coupled with each other and power is transmitted therebetween. In addition, in this electric field coupling scheme, if the amount of power being transmitted is comparatively large and a foreign object is interposed between the electrodes, a malfunction may occur. Accordingly, a wireless power transmission system capable of detecting that a foreign object has come close to an electrode is proposed in Patent Document 1.
In the wireless power transmission system described in Patent Document 1, a foreign object detection electrode is provided in the power transmission device so as to be spaced apart from an electrode used for electric field coupling. A voltage generated between the electric field coupling electrode and the foreign object detection electrode is monitored and when this voltage changes by a certain amount or more, it is determined that a foreign object has come close to the space between the electric field coupling electrodes of the power transmission device and the power reception device and power transmission is stopped.
Patent Document 1: International Publication No. 2012/070479.
However, there is a problem in the case described in Patent Document 1 in that a foreign object detection electrode needs to be provided and additionally the foreign object detection electrode needs to be provided so as to surround an electric field coupling electrode and furthermore the shapes of the electrodes used in the power transmission device are restricted. In addition, there is also a problem in that, if the foreign object detection electrode has a shape containing a cut-out portion, it will not be possible to detect a foreign object when a foreign object approaches the cut-out portion. Consequently, in Patent Document 1, it may not be possible to accurately detect a foreign object and there is a risk of a malfunction occurring due to it not being possible to detect a foreign object with certainty and a user touching the foreign object.